Frontiers in Chemistry

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ISSN / EISSN : 2296-2646 / 2296-2646
Published by: Frontiers Media SA (10.3389)
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Mengdi Zhang, Xuan Zheng, Jiawei Mu, Pengfei Liu, Wenhan Yuan, Shuli Li, Xiaobo Wang, Haiqiu Fang, Haiyan Liu, Tao Xing, et al.
Published: 24 September 2021
Frontiers in Chemistry, Volume 9; https://doi.org/10.3389/fchem.2021.760473

Abstract:
Lithium-ion capacitors (LICs) have been proposed as an emerging technological innovation that integrates the advantages of lithium-ion batteries and supercapacitors. However, the high-power output of LICs still suffers from intractable challenges due to the sluggish reaction kinetics of battery-type anodes. Herein, polypyrrole-coated nitrogen and phosphorus co-doped hollow carbon nanospheres ([email protected]) were synthesized by a facile method and employed as anode materials for LICs. The unique hybrid architecture composed of porous hollow carbon nanospheres and PPy coating layer can expedite the mass/charge transport and enhance the structural stability during repetitive lithiation/delithiation process. The N and P dual doping plays a significant role on expanding the carbon layer spacing, enhancing electrode wettability, and increasing active sites for pseudocapacitive reactions. Benefiting from these merits, the [email protected] composite exhibits excellent lithium-storage performances including high rate capability and good cycling stability. Furthermore, a novel LIC device based on the [email protected] anode and the nitrogen-doped porous carbon cathode delivers a high energy density of 149 Wh kg−1 and a high power density of 22,500 W kg−1 as well as decent cycling stability with a capacity retention rate of 92% after 7,500 cycles. This work offers an applicable and alternative way for the development of high-performance LICs.
Xin Zhao, Meng Li, Linping Jiang, Hua Tang, Youwei Guan
Published: 24 September 2021
Frontiers in Chemistry, Volume 9; https://doi.org/10.3389/fchem.2021.683728

Abstract:
Silver nanowire films are good candidates to be used as transparent conductive films that could be widely utilized in organic photoelectronic devices such as polymer solar cells. However, their application is usually limited, as they are mainly used as top electrode materials; otherwise, they would be prone to complex transferring processes. In this study, we successfully prepared device-level ZnO-covered silver nanowire (AgNWs/ZnO) films. ZnO was prepared by a spray pyrolysis method using zinc-ammonia solution at a relatively low temperature (95°C). The films showed good adhesive properties to the glass substrate, considering it withstood the process of applying polyimide tapes on the surface and tearing them off more than 100 times. It also exhibited good conductivity (∼24 Ω/sq) with high transmittance in the visible range (>80%). After a simple polish and patterning, AgNWs/ZnO showed a good performance as a sub-electrode for polymer solar cells. The PM6:Y6 devices achieved a high power conversion efficiency of 8.37% with an open-circuit voltage of 0.81 V, a short-circuit current density of 18.18 mA/cm2, and a yield of 81.25%. This indicates that the technology has a good prospect of large-scale fabrication of organic photoelectronic devices.
Jun Jin, Linlin Li, Lihui Zhang, Zhihui Luan, ,
Published: 24 September 2021
Frontiers in Chemistry, Volume 9; https://doi.org/10.3389/fchem.2021.748044

Abstract:
As functional nanomaterials with simulating enzyme-like properties, nanozymes can not only overcome the inherent limitations of natural enzymes in terms of stability and preparation cost but also possess design, versatility, maneuverability, and applicability of nanomaterials. Therefore, they can be combined with other materials to form composite nanomaterials with superior performance, which has garnered considerable attention. Carbon dots (CDs) are an ideal choice for these composite materials due to their unique physical and chemical properties, such as excellent water dispersion, stable chemical inertness, high photobleaching resistance, and superior surface engineering. With the continuous emergence of various CDs-based nanozymes, it is vital to thoroughly understand their working principle, performance evaluation, and application scope. This review comprehensively discusses the recent advantages and disadvantages of CDs-based nanozymes in biomedicine, catalysis, sensing, detection aspects. It is expected to provide valuable insights into developing novel CDs-based nanozymes.
Qiong Wang, Yan Wang, Shuang Yang, Changyi Lin, Lateef Aliyu, Yiqun Chen, Lisa Parsons, Yuan Tian, Hongpeng Jia, Andrew Pekosz, et al.
Published: 24 September 2021
Frontiers in Chemistry, Volume 9; https://doi.org/10.3389/fchem.2021.735558

Abstract:
The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus utilizes the extensively glycosylated spike (S) protein protruding from the viral envelope to bind to angiotensin-converting enzyme-related carboxypeptidase (ACE2) as its primary receptor to mediate host-cell entry. Currently, the main recombinant S protein production hosts are Chinese hamster ovary (CHO) and human embryonic kidney (HEK) cells. In this study, a recombinant S protein truncated at the transmembrane domain and engineered to express a C-terminal trimerization motif was transiently produced in CHO and HEK cell suspensions. To further evaluate the sialic acid linkages presenting on S protein, a two-step amidation process, employing dimethylamine and ammonium hydroxide reactions in a solid support system, was developed to differentially modify the sialic acid linkages on the glycans and glycopeptides from the S protein. The process also adds a charge to Asp and Glu which aids in ionization. We used MALDI-TOF and LC-MS/MS with electron-transfer/higher-energy collision dissociation (EThcD) fragmentation to determine global and site-specific N-linked glycosylation patterns. We identified 21 and 19 out of the 22 predicted N-glycosites of the SARS-CoV-2 S proteins produced in CHO and HEK, respectively. It was found that the N-glycosite at 1,158 position (N1158) and at 122, 282 and 1,158 positions (N122, N282 and N1158) were absent on S from CHO and HEK cells, respectively. The structural mapping of glycans of recombinant human S proteins reveals that CHO-Spike exhibits more complex and higher sialylation (α2,3-linked) content while HEK-Spike exhibits more high-mannose and a small amount of α2,3- and α2,6-linked sialic acids. The N74 site represents the most abundant glycosite on both spike proteins. The relatively higher amount of high-mannose abundant sites (N17, N234, N343, N616, N709, N717, N801, and N1134) on HEK-Spike suggests that glycan-shielding may differ among the two constructs. HEK-Spike can also provide different host immune system interaction profiles based on known immune system active lectins. Collectively, these data underscore the importance of characterizing the site-specific glycosylation of recombinant human spike proteins from HEK and CHO cells in order to better understand the impact of the production host on this complex and important protein used in research, diagnostics and vaccines.
Roberta Tabone, Dominik Feser, Enrico D. Lemma, Ute Schepers,
Published: 23 September 2021
Frontiers in Chemistry, Volume 9; https://doi.org/10.3389/fchem.2021.754420

Abstract:
Novel heteroleptic ZnII bis(dipyrrinato) complexes were prepared as intriguing emitters. With our tailor-made design, we achieved far-red emissive complexes with a photoluminescence quantum yield up to 45% in dimethylsulfoxide and 70% in toluene. This means that heteroleptic ZnII bis(dipyrrinato) complexes retain very intense emission also in polar solvents, in contrast to their homoleptic counterparts, which we prepared for comparing the photophysical properties. It is evident from the absorption and excitation spectra that heteroleptic complexes present the characteristic features of both ligands: the plain dipyrrin (Lp) and the π-extended dipyrrin (Lπ). On the contrary, the emission comes exclusively from the π-extended dipyrrin Lπ, suggesting an interligand nonradiative transition that causes a large pseudo-Stokes shift (up to 4,600 cm−1). The large pseudo-Stokes shifts and the emissive spectral region of these novel heteroleptic ZnII bis(dipyrrinato) complexes are of great interest for bioimaging applications. Thus, their high biocompatibiliy with four different cell lines make them appealing as new fluorophores for cell imaging.
Zhicheng Dai, Taotao Ai, Qixin Zhou,
Published: 23 September 2021
Frontiers in Chemistry, Volume 9; https://doi.org/10.3389/fchem.2021.771438

Abstract:
Editorial on the Research TopicDesign, Synthesis, and Application of Novel π-Conjugated Materials—Part II During last few years, new π-conjugated materials have received more and more attention in the community due to their potential wide range of applications such as organic field effect transistors (OFETs), solar cells, sensors and so on. Among them, the works with respect to the design and optimization of π-conjugated molecules have been extensively investigated. This research topic includes 10 articles of reviews and original research works, which describe a series of novel π-conjugated materials along with various applications. These articles provide an overview of different types of π-conjugated materials and of how they are designed and characterized, thereby providing an overview of progress and development direction in this field. Over the last decade, heptazine-based π-conjugated materials, including polymeric graphitic carbon nitride (g-C3N4) and corresponding small molecules, have attracted extensive attention by virtue of intriguing optoelectronic and photocatalytic properties in the fields of organic optoelectronics and photocatalysis. From the perspective of organic electroluminescence (EL), Li and co-workers reported an interesting monomeric heptazine derivative (HAP-3DF) which exhibits enhanced EL via n-π* transition character and exciplex-based thermally activated delayed fluorescence (TADF), respectively (Li et al.). The same group subsequently provided an overview of monomeric and polymeric heptazine-based π-conjugated materials for light-emitting. In this review, the metal ion-containing, polymeric g-C3N4-based, monomeric heptazine-based light-emitting materials and devices are systematically summarized, which is not only beneficial for the future molecular design of high-performance luminescent materials, but also for the acceleration of practical applications of heptazine-based materials and devices (Li et al.). Normally, conjugated materials exhibit strong emission in their solution phase, but showing weak or quenched luminescence in the solid phase due to the aggregation. Ma et al. synthesized the molecules that contain tetrastyrene and benzimidazole structures to obtain molecules (TPEBZMZ) with strong aggregation induced luminescence (AIE) effect. The fluorescent nanofiber membrane, prepared by electrospinning TPEBZMZ and polylactic acid (PLA) blend solution, showed excellent and reversible acid-induced discoloration. This work provides not only a novel AIE material, but also a simple strategy to design the stimulus responsive fluorescent film sensor (Ma et al.). As an interesting electron donor-acceptor material, diketopyrrolopyrrole (DPP)-based donor-acceptor conjugated materials have a very bright prospect in the application of electronic devices, typically in OFET due to their high charge transfer mobility. Zhou et al. reviewed the DPP, iso-DPP and their derivatives-based materials in OFETs, and mentioned that the hole transfer mobility based on the DPP polymers is up to 26 cm2 V−1 s−1. To obtain high-performance DPP-based semiconductor materials, the research direction should focus on not only the modification of the chemical structures on planar materials backbone and large π-convergence system, but also the molecules packing such as strong π-π stacking and aggregation, short molecular distance etc. (Zhou et al.). Bao’s group reviewed hydrogen-bonded materials in OFETs. The authors reviewed a series of small molecules and polymers with hydrogen-bonding association in the application of OFETs, indicating that hydrogen-bonds could not only enable the molecular reassembly to obtain a more ordered crystalline structure and improved π - π stacking, but also reduce the distance of the neighboring molecules and thus increase the molecular packing density. These behaviors could significantly enhance the charge transfer mobility (Shi et al.). Lu et al. also reviewed the conjugated materials in OFETs. and other applications such as organic solar cells (OSCs), sensors, and coating. This article pointed out that there are still a big room for the scientists to explore the highly selective and sensitive sensors. Conjugated polymer coating with multi-functions is also promising and interesting. In addition, the development of novel materials in OSCs with a broad range of light absorption and high charge mobility is still the research trend in the field (Lu et al.). OSCs, as high-quality next-generation energy transfer devices, have attracted extensive attention by researchers. Among them, fullerene acceptors are being replaced by non-fullerene acceptors because of their weak absorption and limited structural modification. Lin et al. synthesized a non-fullerene electron-acceptor cyclized by selenium branched chain based on ring fusion perylene diimide (PDI) tripolymer, and obtained a device with VOC up to 1.12 V. Although the maximum power conversion efficiency (PCE) in this work is only 1.6%, it still provides a feasible idea for seleniding other compounds to improve the performance of OSCs in the future (Lin et al.). Another type of potential photovoltaic device is perovskite solar cells (PSCs). Hole transfer layer (HTL) plays a crucial role in achieving high performance of PSCs. However, the most used HTLs require the dopant to enhance the PCEs of PSCs due to their inherent low conductivity, leading to the decrease of the stability of the PSCs. Thus, the development of dopant-free hole transfer materials (HTM) is one main research trend. Deng et al. reviewed a series of dopant-free HTMs and pointed out that the molecular design concept for high-performance dopant-free HTMs is enlarging the π-conjugation system, increasing the planarity of molecular backbone, and introducing the functional atoms/groups to achieve interfacial interaction between the HTM layer and the perovskite layer, and, which...
Muneerah Mogren Al-Mogren,
Published: 23 September 2021
Frontiers in Chemistry, Volume 9; https://doi.org/10.3389/fchem.2021.751203

Abstract:
CCSD(T)-F12 theory is applied to determine electronic ground state spectroscopic parameters of various isotopologues of methylamine (CH3-NH2) containing cosmological abundant elements, such as D, 13C and 15N. Special attention is given to the far infrared region. The studied isotopologues can be classified in the G12, G6 and G4 molecular symmetry groups. The rotational and centrifugal distortion constants and the anharmonic fundamentals are determined using second order perturbation theory. Fermi displacements of the vibrational bands are predicted. The low vibrational energy levels corresponding to the large amplitude motions are determine variationally using a flexible three-dimensional model depending on the NH2 bending and wagging and the CH3 torsional coordinates. The model has been defined assuming that, in the amine group, the bending and the wagging modes interact strongly. The vibrational levels split into six components corresponding to the six minima of the potential energy surface. The accuracy of the kinetic energy parameters has an important effect on the energies. Strong interactions among the large amplitude motions are observed. Isotopic effects are relevant for the deuterated species.
, Gareth Waters, Serban Moldoveanu, Jennifer Margham, Anthony Cunningham, Carl Vas, Andrew Porter, Helena Digard
Published: 23 September 2021
Frontiers in Chemistry, Volume 9; https://doi.org/10.3389/fchem.2021.742538

Abstract:
Background: Concerns over the presence of the diketones 2,4 butanedione (DA) and 2,3 pentanedione (AP) in e-cigarettes arise from their potential to cause respiratory diseases. Their presence in e-liquids is a primary source, but they may potentially be generated by glycerol (VG) and propylene glycol (PG) when heated to produce aerosols. Factors leading to the presence of AP, DA and acetoin (AC) in e-cigarette aerosols were investigated. We quantified direct transfer from e-liquids, examined thermal degradation of major e-liquid constituents VG, PG and 1,3 propanediol (1,3 PD) and the potential for AC, AP and DA production from sugars and flavor additives when heated in e-cigarettes. Method: Transfers of AC, AP and DA from e-liquids to e-cigarette aerosols were quantified by comparing aerosol concentrations to e-liquid concentrations. Thermal generation from VG, PG or 1,3 PD e-liquids was investigated by measuring AC, AP and DA emissions as a function of temperature in an e-cigarette. Thermal generation of AC, AP and DA from sugars was examined by aerosolising e-liquids containing sucrose, fructose or glucose in an e-cigarette. Pyrolytic formation of AP and DA from a range of common flavors was assessed using flash pyrolysis techniques. Results: AC transfer efficiency was >90%, while AP and DA were transferred less efficiently (65%) indicating losses during aerosolisation. Quantifiable levels of DA were generated from VG and PG, and to a lesser extent 1,3 PD at coil temperatures >300°C. Above 350°C AP was generated from VG and 1,3 PD but not PG. AC was not generated from major constituents, although low levels were generated by thermal reduction of DA. Aerosols from e-liquids containing sucrose contained quantifiable (>6 ng/puff) levels of DA at all sucrose concentrations tested, with DA emissions increasing with increasing device power and concentration. 1% glucose, fructose or sucrose e-liquids gave comparable DA emissions. Furanose ring compounds also generate DA and AP when heated to 250°C. Conclusions: In addition to less than quantitative direct transfer from the e-liquid, DA and AP can be present in the e-cigarette aerosol due to thermal decomposition reactions of glycols, sugars and furanonse ring flavors under e-cigarette operating conditions.
Zhen Zuo, Lifen Liang, Qianqian Bao, Pengtao Yan, Xin Jin, Yulin Yang
Published: 23 September 2021
Frontiers in Chemistry, Volume 9; https://doi.org/10.3389/fchem.2021.740447

Abstract:
During the friction process, the polytetrafluoroethylene (PTFE) adhered on the counterpart surface was known as the PTFE transfer film, which was fundamental to the lubricating performance of the PTFE. However, the adhesive interaction between the iron surface and the adhered PTFE transfer film is still unclear. In present study, molecular dynamics simulations were used to reveal the adhesive interaction between the iron surface and PTFE transfer film. Based on the atomic trajectories obtained through the molecular dynamics, the interaction energy, concentration profile, radial distribution function, and mean square displacement were calculated to analyze the structure of the interface. The negative values of the interaction energy demonstrated the adhesive interaction between the PTFE transfer film and Fe surfaces, resulting in the accumulation of the PTFE transfer film on the Fe surface. Among the (100) (110), and (111) surfaces of α-Fe (110) surface owns the strongest adhesive interaction with the PTFE transfer film. Compared with the original PTFE molecule, the chain broken PTFE, hydroxyl substituted PTFE, and carbonyl substituted PTFE exhibited stronger adhesive interaction with Fe surface. The adhesive interaction between the PTFE transfer film and Fe surfaces was mainly originated from the Fe atoms and the F atoms of the adsorbate PTFE transfer film, which was governed by the van der Waals force. The bonding distance between the Fe atom and the F atom of the adsorbate PTFE transfer film is around 2.8 Å. Moreover, the chain broken of PTFE molecule and the rise of temperature can remarkably increase the mobility of polymer chains in the interface system.
Chao Ma, Mohammed S. Taghour, , Ahmed B. M. Mehany, Naglaa Mostafa, Ahmed Nabeeh, Ibrahim H. Eissa,
Published: 22 September 2021
Frontiers in Chemistry, Volume 9; https://doi.org/10.3389/fchem.2021.725135

Abstract:
Guided by the structural optimization principle and the promising anticancer effect of the quinoxaline nucleus, a new series of novel HDAC inhibitors were designed and synthesized. The synthesized compounds were designed to bear the reported pharmacophoric features of the HDAC inhibitors in addition to an extra moiety to occupy the non-used vacant deep pocket of the HDAC receptor. The newly prepared compounds were evaluated for their in vitro anti-proliferative activities against HepG-2 and HuH-7 liver cancer cell lines. The tested compounds showed promising anti-proliferative activities against both cell lines. The most active ten candidates (6 c , 6 d , 6 f , 6 g , 6 k , 6 l , 7 b , 8, 10 h , and 12) were further evaluated for their effect on the gene expression levels of Bax as an apoptotic marker and Bcl-2 as an anti-apoptotic one. Moreover, they were evaluated for their ability to inhibit histone deacetylase (HDAC1, HDAC4, and HDAC6) activities. Compound 6 c achieved the best cytotoxic activities on both HepG-2 and HuH-7 cell lines with IC50 values of 1.53 and 3.06 µM, respectively, and also it showed the most inhibitory activities on HDAC1, HDAC4, and HDAC6 with IC50 values of 1.76, 1.39, and 3.46 µM, respectively, compared to suberoylanilide hydroxamic acid (SAHA) as a reference drug (IC50 = 0.86, 0.97, and 0.93 µM, respectively). Furthermore, it achieved a more characteristic arrest in the growth of cell population of HepG-2 at both G0/G1 and S phases with 1.23-, and 1.18-fold, respectively, compared to that of the control, as determined by cell cycle analysis. Also, compound 6 c showed a marked elevation in the AnxV-FITC apoptotic HepG-2 cells percentage in both early and late phases increasing the total apoptosis percentage by 9.98-, and 10.81-fold, respectively, compared to the control. Furthermore, docking studies were carried out to identify the proposed binding mode of the synthesized compounds towards the prospective target (HDAC4). In silico ADMET and toxicity studies revealed that most of the synthesized compounds have accepted profiles of drug-likeness with low toxicity. Finally, an interesting SAR analysis was concluded to help the future design of more potent HDACIs in the future by medicinal chemists.
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